It has previously been suggested in U.S. Pat. No. 3,536,577 to effect bleaching of cellulosic fibrous material, particularly wood pulp, using an aqueous solution of chlorine dioxide and chlorine at moderate temperatures up to 35.degree. C. In this process, the chlorine dioxide constitutes about 20 to about 95% of the total available chlorine of the solution.
It has also previously been found that the characteristics of the pulp bleached by the latter process can be improved by applying the chlorine dioxide and chlorine sequentially instead of as a mixture of the two, without an intermediate washing between the two bleaching chemical applications, as described in U.S. Pat. Nos. 3,433,702 and 3,501,374.